1. Technical Field
The invention relates to tire building equipment and in particular to the tire building drum and inflatable turn-up bladder associated therewith. More particularly, the invention relates to an improved inflatable bladder which reduces or eliminates cord length variation of the tire carcass on the drum by stabilizing the bladder in the area utilized for lifting the reinforced cord fabric of the tire carcass to the tire bead on the tire building drum.
2. Background Information
In the building of pneumatic tires, the various sheets or strip components thereof are laid and placed around a cylindrical drum to build up the carcass. Generally these sheets consist of an innerliner, reinforcement strips of calendered fabric, steel, fiberglass or the like, sidewall strips, etc. One of the steps in the tire manufacturing process is the coaxial telescopic mounting of a bead ring over the drum around which the ends of the tire carcass are turned up in forming the usual toroidal shape of the final tire. These carcass ends are generally turned up by inflatable bladders which are sleeve-like, the ends of which are sealingly mounted on the drum with the intermediate area being inflatable by air for rolling up the ends of the tire carcass around the bead rings. Prior to the inflation of the turn-up bladders, the carcass is moved radially outwardly into engagement with the telescopically located bead rings by a plurality of circularly arranged bead lock segments which are mounted on the drum and are expanded radially outwardly by pressurized air, mechanical linkages or the like.
However, when the bead locks are actuated, there is a lateral displacement of the bladders due to the bead lock expansion which results in an axial shift of the carcass ply material, and in particular an axial shift of the reinforcing fabric or cord thereof at variable rates around the circumference of the drum, thereby producing cord length variations. These cord length variations in the final tire may produce undesirable characteristics, particular in the smoothness of the ride provided by the tire.
Therefore, the need has existed for an improved inflatable bladder for a tire building drum which will turn-up the ends of the tire carcass around the bead after locking the bead in place, without producing cord length variations due to the heretofore lateral or axial movement of the inflatable bladder and tire carcass laid thereon. Various tire building equipment, using inflatable bladders have been developed, none of which are believed to overcome the lateral movement problem of the bladder and reinforcing portion of the tire carcass as does the present invention.
The most pertinent known prior art to the present invention is set forth in the following patents:
U.S. Pat. No. 3,101,289 discloses a method of making a resilient reinforced diaphragm for use on a tire building drum wherein the diaphragm has lateral zones and a central zone, with the central zone having reinforcing material embedded therein. Upon expansion of a pair of rings, the bead wires are pressed into grooves formed in the rings with the reinforcing material in the central zone, being used to provide radial stability to the diaphragm.
U.S. Pat. No. 3,418,192 shows the use of a bellows secured to the drum at the enlarged bead portions thereof in a tire building drum.
U.S. Pat. No. 3,989,564 discloses a method and apparatus for forming a tire using a building drum that employs an inflatable bladder wherein the expandable sleeve thereof has an inflatable portion that is formed from a rubber material without cord reinforcement and is retained in a slot by an integral flange. This is a type of construction utilized for many tire building drums for holding the sleeve on the center of the drum when radially expanding the drum.
U.S. Pat. No. 4,081,310 discloses an expandable bead grip wherein one bead end portion of the bladder is retained in a groove formed in the expandable bead ring.
U.S. Pat. No. 4,830,693 shows another inflatable bladder used in a tire building drum which has reinforcing material embedded in a portion thereof.
U.S. Pat. No. 4,450,025 discloses a method and apparatus for encasing a tire bead wherein an inflatable bladder is positioned over drum segments via a plurality of projections spaced at intervals around a circumference of the drum with projections fitting into grooves. Even though the projections prevent axial movement of the bladder, it does not solve the same problem as that solved by the present invention, that is, cord length fabric variations upon outward expansion of the bead lock segments. In this prior art patent, the bead cover strip does not move laterally and the projections are only spaced at intervals around the circumference of the drum.
Although the known prior art discloses various inflatable bladders and expandable bead lock segments, none of these provide a construction which solves the problem of cord length variation upon the outward expansion of the bead lock segments due to the lateral displacement of the bladder and supported tire carcass.